Los Alamos National Laboratory

Los Alamos National Laboratory

Delivering science and technology to protect our nation and promote world stability

Developing the Annual Assessment

Though penned in the director’s office, the annual weapons assessment letter is the result of an entire Laboratory workforce.
October 1, 2018
Terry Wallace

Director Terry Wallace at his desk. To learn more about the annual assessment, read the National Defense Authorization Act for Fiscal Year 2003, P.L. 107-314, section 3141.


"Los Alamos has spent the 26 years since the end of nuclear testing developing the tools required to understand at the subatomic level what happens to materials and components as they age."- Terry Wallace

By Terry Wallace, Laboratory director

On September 23, 1992, the United States conducted Divider, an underground test at the Nevada Test Site. The Los Alamos–designed test was the nation’s 1,030th—and final—nuclear weapons test, marking the end of an era that began with the Trinity test 47 years prior.

In 1995, President Clinton announced the intent to sign the Comprehensive Test Ban Treaty (CTBT), which would permanently eliminate testing, with a caveat: The United States reserved the right to withdraw from the CTBT for reasons of supreme national interest.

The cessation of nuclear testing presented an extraordinary challenge: With no full-scale nuclear testing, how could the nation know that our nuclear weapons would work?

As stockpile stewardship—a science-based program of experiment and simulation to replace actual testing—developed, so did an annual assessment process that requires the Laboratory directors at Los Alamos, Livermore, and Sandia to complete an assessment of the safety, reliability, and performance of each nuclear weapon type in the active stockpile.

Los Alamos and Sandia jointly develop and issue annual assessment reports on each warhead and bomb for which they are responsible—the B61, W76, W78, and W88. These warheads, however, are decades old. How can we be confident that an aging warhead will still deliver the expected results?

The answer lies in the Laboratory’s extensive expertise in modeling and simulation, physics, chemistry, and a whole host of other scientific and technological capabilities. Los Alamos has spent the 26 years since the end of nuclear testing developing the tools required to understand at the subatomic level what happens to materials and components as they age. It is this information that feeds into the annual assessment and allows me to conclude, with confidence, that the nation’s strategic nuclear deterrent is reliable.

One of my most important jobs as director of Los Alamos National Laboratory is to provide this assessment, which comes in the form of letter to the president (via the secretaries of Energy and Defense) every September. The specifics in the letter cannot be changed by anyone once it is issued from Los Alamos. 

The letter contains a statement regarding the ability to maintain warhead and bomb certification in the absence of nuclear testing that is backed up with a summary of current issues. The letter also discusses the science-based tools and methods, adequacy of the nuclear weapons production complex, readiness to conduct nuclear testing, and other information. The president has until March 15 to forward the letter and any comments to Congress.

Although many people have heard of the annual assessment letter, it is not something frequently discussed in detail—which can lead some to believe only a few people at the Laboratory work on it. That could not be further from the truth. Everyone who works at the Laboratory, regardless of position, impacts the annual weapons assessment.

Stewardship of the nuclear stockpile is our primary mission as the nation’s premier nuclear weapons laboratory and, thus, all of our work supports it. Whether an employee is a weapons designer, a computer coder, an administrative assistant, or a member of the janitorial staff, his or her work supports the annual assessment.  


Technical Area 3 at the Laboratory.

This summer, I received detailed technical briefings from the warhead managers and the Weapons Programs division leaders about the state of the Laboratory’s nuclear weapons systems. My independent Red Team for annual assessment (comprised of nuclear weapons experts from Los Alamos, Sandia, and Livermore) and Livermore’s independent assessment teams briefed me on their assessment of the safety, reliability, and performance of Los Alamos’ nuclear weapons systems.

After listening to these briefings, I can say, once again, what an outstanding team we have here at the Laboratory. The ingenuity, dedication, and critical thinking of our staff continuously impress me. It is because of these people that I confidently signed my name to the annual assessment letter that will help inform the highest leaders in government.

It is my honor to lead this Laboratory, and I thank all Los Alamos employees for their work supporting our mission to serve the nation.